I installed a Zimbra 8.0.2 (Edit: FOSS) on a Ubuntu Server 12.04 from scratch.
I need to relay/authenticate outgoing mails which has been setup according to Outgoing SMTP Authentication - Zimbra :: Wiki (Working well on Zimbra 7).
However, after setting relaying up, outgoing mail would still be returned with "Relay access denied (in reply to RCPT TO command)".

After digging aroud, I compared /opt/zimbra/postfix/conf/main.cf and found the